I. Field of the Invention
The present invention is directed to solid delivery systems which at body temperature exhibit controlled release and bioadherence characteristics. Specifically, the invention is concerned with solid delivery systems that are formed from and whose internal phase is greater than that of the external phase which are water in oil in nature.
II. Description of the Prior Art
High internal phase ratio emulsions, those whose internal phase is greater than 70%, have been discovered to exhibit bioadherent properties. Such emulsions are described in U.S. Pat. No. 4,551,148. It generally is known that such systems are thixotropic liquids or semi-solids. The emulsions in their most viscous state resemble an ointment or cream.
Under certain circumstances it is preferable to deliver active agents through a solid which melts at body temperature. However, it is generally recognized that water should be avoided in the formulation of these solids. Reasons for the avoiding of water in such systems are well known and are discussed in The Theory and Practice of Industrial Pharmacy, Lachman et al, 1976, page 264 and Senior, Rectal Administration of Drugs, Advances in Pharmaceutical Sciences, edited by Beckett et al, Vol. 4, 1974, page 367. Conventional systems do not include more than 20% water when long term stability is required and usually about 10%. Formulations have been produced with as much as 40% water but such products demonstrate only short term stability.
It is an object of the invention to provide a system which comprises a high or internal phase ratio emulsion, at least 60% internal phase, in a solid form that at body temperature exhibits controlled release and bioadherent characteristics. It is a further object of the invention to provide a drug delivery system which does not draw moisture from tissues. Finally, it is an object of the invention to provide a delivery system which does not leak from the body orifice.